Reland Use CopyOnWriteBuffer instead of Buffer to avoid unnecessary copies.

webrtc/pc/channel_unittest.cc

 /*
  *  Copyright 2009 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 2751 matching lines @@
 TEST_F(DataChannelTest, TestSendData) {
   CreateChannels(0, 0);
   EXPECT_TRUE(SendInitiate());
   EXPECT_TRUE(SendAccept());
 
   cricket::SendDataParams params;
   params.ssrc = 42;
   unsigned char data[] = {
     'f', 'o', 'o'
   };
-  rtc::Buffer payload(data, 3);
+  rtc::CopyOnWriteBuffer payload(data, 3);
   cricket::SendDataResult result;
   ASSERT_TRUE(media_channel1_->SendData(params, payload, &result));
   EXPECT_EQ(params.ssrc,
             media_channel1_->last_sent_data_params().ssrc);
   EXPECT_EQ("foo", media_channel1_->last_sent_data());
 }
 
 // TODO(pthatcher): TestSetReceiver?